Thelonectria

Thelonectria is a genus of fungi belonging to the Ascomycota phylum, responsible for causing severe necrosis and canker diseases in various woody plants. As a plant pathogen, it primarily targets the bark and vascular tissues, leading to the formation of lesions that can girdle branches or stems, eventually causing the death of the affected plant tissue.

This disease commonly affects fruit trees, such as apples and pears, as well as various deciduous forest species. The pathogen enters the plant host primarily through wounds, including those caused by frost cracking, sunscald, insect damage, or improper pruning cuts, which serve as entry points for the fungal mycelium to colonize the inner bark and cambium.

Symptoms of Thelonectria infection are characterized by the appearance of depressed areas on the bark, which later develop into distinct cankers. As the fungus spreads, the bark may crack and reveal the underlying wood. During moist conditions, small orange or red fungal fruiting bodies, known as perithecia, emerge on the dead bark surface, confirming the active presence of the pathogen.

The development and dispersal of the fungus are favored by high humidity and moderate temperatures, which facilitate the production and release of spores. These spores are spread by wind, splashing rain, or pruning tools. The pathogen is highly resilient, capable of overwintering within the bark of infected trees or on plant debris, ensuring a persistent threat to orchard health.

Effective management and prevention of Thelonectria require a structured approach:

• Prompt excision and removal of infected branches, ensuring cuts are made into healthy, living wood.
• Disinfection of all pruning tools between each cut to prevent cross-contamination.
• Application of protective fungicides, particularly copper-based formulations, during dormant periods.
• Maintenance of tree vigor through proper fertilization and watering to minimize susceptibility to infection.